In the past, a number of blade positioning devices have been proposed for use in motor graders. One such device used a beam member saddling the main frame of the grader and rigidly attached to it. Two hydraulic lift cylinders laterally spaced of the main frame were supported by the beam member and the other end of the cylinders attached to a draw bar swivellably fastened to the forward portion of the grader. The device used a hydraulic shift cylinder fastened to the draw bar and the main frame allowing the draw bar to be positioned either side of the grader. The lift cylinder could then be adjusted to control the elevation and inclination of the scraper blade. However, because this transverse beam was rigidly attached to the main frame of the grader, the degree of inclination of the blade was limited to interference of the cylinders with the main frame.
This particular problem of interference was overcome by mounting the transverse beam on a large ring bearing surrounding the frame of the grader. This arrangement allowed the beam to rotate relative to the mainframe of the grader and lock at various adjusted positions. The apparatus, however, introduced new problems in that this large ring bearing was expensive to manufacture and vulnerable to wear. Other problems also occurred with shearing of the locking pin used to maintain the adjusted position of the beam; however, this problem was overcome by using several lock pins. As the wear of the ring bearing increased, the performance of the grader decreased. Repair of the ring bearing was difficult to accomplish as well as expensive.
Operator visibility and flexibility of the blade positioning system are extremely important and designs have often maximized one of these functions to the detriment of the others. German Offenlegungschrift No. 1,484,689 discloses a one-piece construction blade positioning apparatus, which surrounds the frame and is pivoted to the upper surface thereof with a lock pin arrangement located beneath the frame. However, the portion of the structure immediately adjacent and to either side, the pivot point arcs upwardly and outwardly thereby seriously impeding the operator's visibility once the structure has been rotated to allow the blade to be positioned for bank sloping. In its maximum position, the area immediately above the center of the frame has become quite congested, thereby seriously impeding the operator's visibility. It is desirable in blade positioning systems to have the area above the frame of the grader as free from obstruction as possible; however, this requirement has not been satisfied by prior art rigid systems.
Other mechanism include the use of two pivoted crank arms secured to the opposite vertical faces of the main frame and joined by a link member. These pivot arms also support the hydraulic lift cylinders and the arrangement functions essentially as a four bar linkage. Although these systems are an improvement over the large ring bearing method described above, they still suffer from many of the same problems, due to the relatively large number of moving parts and the required tolerances associated with each pivot point.
The main problems in prior art structures are the high cost to manufacture and maintain the vulnerability of the apparatus to wear, because of the relatively large number of moving parts and the adverse effect they have on visibility looking along the upper frame of the grader.
As wear in the blade positioning apparatus increases, not only the static forces but dynamic forces must also be considered. The inertia forces are considerable with such large devices and, therefore, the rate of wear accelerates as wear increases. The loads exerted on the blade positioning device are high and often have impact loads of much higher magnitude due to a sudden change in composition of the ground being graded. These high loads and higher impact loads demand a system that is inherently strong and also easy to repair.
Another problem common to these prior art systems is the lock mechanism, which normally includes a lock pin for engagement in an aperture provided in one compound of the blade positioning structure. Due to the high loads that can be encountered and due to wear, damage of the pin may result which can cause difficulties in releasing and locking of this mechanism. Furthermore, if the blade positioning structure remains in one position for an extended period of time, corrosion may result seizing the pin in place. The present invention includes a unique lock mechanism for overcoming a number of these problems.